Eyelashes have evolved as a protective feature for the eyes, offering defense against external dangers such as contamination, excessive evaporation, and shear stress from airflow. They may also serve as indicators of an individual’s health, since various diseases, both congenital and non-congenital, can influence eyelash length. […]

this research primarily focused on the attractiveness of eyelash length […] investigating perceptions of health and sexual receptivity as functions of eyelash length, hypothesizing that while long eyelashes may be rated as less attractive, they could be perceived as signals of sexual receptivity. […]

results showed that eyelash length is positively associated with perceived sexual receptivity, suggesting that longer eyelashes might signal openness to casual relationships, despite lower attractiveness and health ratings at lengths beyond the optimal one-third ratio

{ Archives of Sexual Behavior | Continue reading }

Previous research has found that mothers are more likely to ascribe paternal resemblance to newborns. Moreover, studies have found that fathers who perceive that their children resemble them invest more in those children. In this study, we aimed to examine if maternal claims of paternal resemblance exist even with very limited visual information by asking parents whom they believed the fetus looked like during an ultrasound. We found that mothers, but not fathers, were more likely to say that the fetus resembled the father.

{ Evolution and Human Behavior | Continue reading }

The frequently repeated view that men are attracted to women with low waist–hip ratios (WHRs) and low body mass indices (BMI) (in well-nourished populations) because these traits indicate health and fertility does not appear to be well supported. Indeed, a low WHR and BMI are most likely to occur in young women in their late teens who have never been pregnant (nulligravidas), women who have demonstrably lower fertility and greater liability to infection than women in their 20s. […]

A nubile woman is a nulligravida who has recently completed physical growth, puberty, and sexual development. This is usually accomplished 3–4 years after menarche in the mid to late teens when female reproductive value is maximal. As noted, women in the nubile age group have the lowest WHRs and, in well-nourished populations, have lower BMIs than women in their 20s, traits strongly associated with attractiveness. […]

Using data for 1.7 million first births from 1990 U.S. natality and mortality records, we compared outcomes for women with first births (primiparas) aged 16–20 years (when first births typically occur in forager and subsistence groups) with those aged 21–25 years. The younger primiparas had a much lower risk of potentially life-threatening complications of labor and delivery and, when evolutionarily novel risk factors were controlled, fetuses which were significantly more likely to survive despite lower birth weights.

{ Evolutionary Psychology | Continue reading }

Unrealistic optimism or optimism bias—the tendency for individuals to overestimate the chance of favorable outcomes occurring and underestimate the chance of bad —has been found to be one of the most pervasive human traits across many domains. For instance, research has shown that individuals tend to underestimate the likelihood of developing a drinking problem or getting divorced and to overestimate their future earnings and how long they are going to live. Our established tendency toward unrealistic optimism poses an evolutionary puzzle as normative models of human judgment, like expected utility theory, suggest unbiased assessments of probabilities are advantageous. Like any other judgmental bias, optimism bias distorts the decision-making process, leading to systematic decision errors, increased rash and risky behavior and a failure to take precautionary measures. […]

There are reasons for expecting that the optimism bias may be associated with cognitive ability. Supportive empirical evidence for this framework comes from the experimental literature on cognitive ability and judgmental biases. For instance, intelligence has been found to lower one’s susceptibility to hindsight bias, overconfidence, framing, and the sunk cost fallacy. […]

we used an unbalanced panel of 36,312 respondents […]

The findings we present provide evidence that forecasting accuracy is linked to cognitive ability. Specifically, we find that higher cognitive ability is associated with a higher incidence of realism and pessimism in beliefs and a lower incidence of unrealistic optimism.

Taken together, our results lead us to conclude that the rash and risky behaviors associated with excessive optimism may be a side product of the true driver, low cognitive ability.

{ Personality and Social Psychology Bulletin | Continue reading }

The present studies investigated the relationships between men’s perceived risk of experiencing sperm competition (i.e., when the ejaculates of two or more men simultaneously occupy the reproductive tract of a single woman), and their use of strategies to detect, prevent, and correct their partner’s sexual infidelity.

We investigated these associations using self-reports provided by men (Study 1, n = 113), partner-reports provided by women (Study 2, n = 136), and dyadic reports (Study 3, n = 103 couples).

The results of these studies indicated that the attractiveness of women was consistently associated with men’s use of benefit-provisioning mate retention behaviors (e.g., buying expensive gifts for one’s partner, showing signs of physical affection) and semen-displacing behaviors (e.g., deeper copulatory thrusting, more thrusts during copulation), whereas the infidelity risk of women was often associated with men’s use of cost-inflicting mate retention behaviors (e.g., threatening to end the relationship, monopolization of partner’s free time).

{ Evolutionary Psychology | Continue reading }

Previous work provides evidence of adaptations to sperm competition in men. For example, men’s testes size relative to body weight is larger than for the monandrous gorilla, which experiences very low sperm competition risk. However, men’s relative testes size is smaller than that of chimpanzees, whose polygynandrous mating system generates substantial sperm competition. […]

Several studies provide evidence that men unconsciously increase sperm number in an ejaculate when they are at greater sperm competition risk. Specifically, men who spent a greater proportion of time apart from their partners since the couple’s last copulation (time during which a man cannot account for his partner’s sexual behavior) produce more sperm in their next in-pair copulatory ejaculate. […]

Researchers have also theorized that the morphology of the human penis suggests an evolved function as a semen displacement device. […]

Both sexes reported that men thrust more deeply and more quickly at the couple’s next copulation when they experienced contexts in which sperm competition is more likely to occur. […] Goetz and colleagues also found that as sperm competition risk increased, men performed more copulatory behaviors that might act to displace the sperm of a potential rival that may be present (such as more thrusts and deeper thrusts during copulation). […]

Symons (1979) argued that women’s orgasm and associated physiological structures such as the clitoris are byproducts of selection on male genitalia and orgasm. […] Research also indicates that orgasm increases the retention of sperm. […] ancestral men who were particularly interested in the occurrence of their partner’s copulatory orgasm may have been more successful in the context of sperm competition.

{ Personality and Individual Differences (2010) | Continue reading }

The infidelity-detection hypothesis for oral sex proposes that men perform oral sex to gather information about their partner’s recent sexual history. […] men at a greater recurrent risk of sperm competition expressed greater interest in, and spent more time performing, oral sex on their partner

{ Personality and Individual Differences (2012) | Continue reading | More: Is Cunnilingus-Assisted Orgasm a Male Sperm-Retention Strategy? }

Nimrod, the builder of cities from Babel to Calah, was the first “mighty man” on earth, and a “mighty hunter before the Lord.” So were other African, Asian, European, and New World kings. They hunted everything from lions to guanacos, on four of the six continents, from the beginning of recorded time. But why?

Hunting provided meat, and it may have also provided military exercises; but most kings subsisted on domesticated animals and plants and delegated their wars to specialists. […]

Hunting was extremely expensive. Kings lost time with their ministers and with their families; they spent enormous resources on elephants and horses, hounds, hawks, manpower, and fodder. In addition to the obvious time and money costs, there were huge risks. Hunting kings and their sons were often wounded. And more than a few died. […]

Some were felled by stray arrows, whereas others were felled by their own arrows; some caught cold in the forest, and others fell off their horses. It is impossible to quantify the time and money costs or the morbidity and mortality risks. However, a list of anecdotes is impressive: Plenty of kings were wounded or killed chasing game in the woods. […]

The benefits seem to have been outweighed by the costs. […]

Evolutionary psychology is predicated on the assumption that humans are collections of vestiges; that Pleistocene ecologies shaped our mental and physical traits, which are often at odds with modern environments, and maladaptive behaviors resulted. Hunting was the human adaptation on the savannah for hundreds of thousands of years. Good hunters won mates by providing meat; or they attracted them by showing off the talents involved in killing game. Human bodies and minds should have been shaped to reflect those facts.

{ Cross-Cultural Research | PDF }

image { Horse Laughs (1891) }

if being very smart was much, much better than being of average smarts, then everyone would [have] become very smart up to the physiological limit. […] The fact that being very intelligent is not evolutionarily clearly “good” seems ridiculousness to many people who think about these things. […]

let’s talk about another quantitative trait which is even more heritable than intelligence, and easier to measure: height. […] Though being a tall male seems in most circumstances to be better in terms of physical attractiveness than being a short male, circumstances vary, and being too tall increases one’s mortality and morbidity. Being larger is calorically expensive. Large people need to eat more because they have larger muscles. […]

let’s go back to intelligence. What could be the trade-offs? First, there are now results presented at conferences that very high general intelligence may exhibit a correlation with some mental pathologies. Though unpublished, this aligns with some prior intuitions. […] Additionally […] one could argue that being too deviated from the norm might make socialization and pair-bonding difficult.

{ GeneExpression | Continue reading }

photo { Linda Evangelista photographed by Philip Tracy for Vogue, January 1992 }

Two years ago a New Scientist headline announced the “world’s first baby born with new ‘3 parent’ technique.” Whereas an embryo is usually produced by one sperm and one egg, this technique uses genetic material from three separate people. First performed by a New York fertility clinic in Mexico to evade US legal restrictions, the procedure has now been replicated several times. […]

Two cases in the UK and Mexico involve a woman who carries a rare disease of her mitochondria, the cellular structures that produce energy in our cells. Mitochondria have their own DNA and can harbor their own genetic diseases. These are passed on solely through the maternal line, because mitochondria are found in eggs but not in sperm. One approach to blocking transmission of these illnesses involves inserting the DNA-filled nucleus from the egg of the woman into a donor egg full of healthy mitochondria but stripped of its own nucleus. Fertilize that hybrid egg with a sperm, and presto! A child could be born nine months later with DNA from three people and without a catastrophic mitochondrial disorder. […] Children conceived with a third person’s mitochondria are, it follows, the offspring of three parents. […]

Mitochondria, it turns out, were originally bacteria; their free-wheeling existence came to an end one day deep in evolutionary history when they entered another single-celled organism and started a new life inside. […]

This is not what we think of as Darwinian evolution, the transmission of genes and traits down the family line. DNA, it turns out, can also be passed laterally, between individuals, including those of different species. […] We may like to think of DNA as the neat bequest of our parents, the fusion of two unique, circumscribed human lineages.  Yet it is—and we are—something more: short strands within a vast interwoven genetic web, stretching back to the earth’s earliest days, linking all living things. 

{ New Republic | Continue reading }

[L]ife may have been seeded here on Earth by life-bearing comets as soon as conditions on Earth allowed it to flourish (about or just before 4.1 Billion years ago). […]

Evidence of the role of extraterrestrial viruses in affecting terrestrial evolution has recently been plausibly implied in the gene and transcriptome sequencing of Cephalopods. The genome of the Octopus shows a staggering level of complexity with 33,000 protein-coding genes more than is present in Homo sapiens. Octopus belongs to the coleoid sub-class of molluscs (Cephalopods) that have an evolutionary history that stretches back over 500 million years, although Cephalopod phylogenetics is highly inconsistent and confusing. Cephalopods are also very diverse, with the behaviourally complex coleoids, (Squid, Cuttlefish and Octopus) presumably arising under a pure terrestrial evolutionary model from the more primitive nautiloids. However the genetic divergence of Octopus from its ancestral coleoid sub-class is very great, akin to the extreme features seen across many genera and species noted in Eldridge-Gould punctuated equilibria patterns (below). Its large brain and sophisticated nervous system, camera-like eyes, flexible bodies, instantaneous camouflage via the ability to switch colour and shape are just a few of the striking features that appear suddenly on the evolutionary scene. The transformative genes leading from the consensus ancestral Nautilus to the common Cuttlefish to Squid to the common Octopus are not easily to be found in any pre-existing life form — it is plausible then to suggest they seem to be borrowed from a far distant “future” in terms of terrestrial evolution, or more realistically from the cosmos at large. Such an extraterrestrial origin as an explanation of emergence of course runs counter to the prevailing dominant paradigm. […]

One plausible explanation, in our view, is that the new genes are likely new extraterrestrial imports to Earth — most plausibly as an already coherent group of functioning genes within (say) cryopreserved and matrix protected fertilized Octopus eggs. […]

Hoyle and Wickramasinghe thus argued and predicted on the basis of the then available evidence that microorganisms and virus populations in the comets and related cosmic bolides appear to have regularly delivered living systems (organisms, viruses and seeds) to the Earth since its formation, and continue to do so. […]

Darwinian evolution and its various non-Darwinian terrestrial drivers are therefore most likely caused by the continuing supply of new virions and micro-organisms from space with their genetic impact events written all over our genomes. Indeed a strong case can be made for hominid evolution involving a long sequence of viral pandemics, each one of which was a close call to total extinction of an evolving line. The most crucial genes relevant to evolution of hominids, as indeed all species of plants and animals, seems likely in many instances to be of external origin, being transferred across the galaxy largely as information rich virions. In some cases it is possible to imagine multicellular life-forms that were established on an icy cometary or planetary body to be transferred as frozen eggs, embryos or seeds in large icy bolides that have been transported to the Earth in soft landings.

{ Progress in Biophysics and Molecular Biology | PDF }

photo { Ezra Stoller, Philip Morris headquarters, Richmond, 1972 }

There is no robust evidence of nonhuman suicides, notwithstanding countless opportunities for such self-killings, if they occurred, to be documented by the world’s farmers, animal breeders, naturalists, and scientists. We are left with anecdote and fable, including the scorpion’s self-sting, proffered by Peña-Guzmán as an example of animal suicide despite clear evidence that scorpions cannot sting themselves to death.

Scorpions are immune to their own venom, presumably because selection has eliminated the germ lines of scorpions that were not so protected. The ubiquity of such specific, self-preserving adaptations connects to a third, theoretical, problem with animal suicide: the absence of a coherent explanation as to how selection could favour and maintain such a capability. […]

Suicide is not observed in nonhumans for a straightforward evolutionary reason: any genes that permitted suicide would have been eliminated along with the suicides’ bodies. Any animal that, in the absence of restraints, was capable of escaping its pain and suffering by self- killing would be expected to seize the opportunity, because some pain is unavoidable in the Malthusian theatre in which selection plays out, and because pain is designed to motivate action to escape. A suicidal animal, if it appeared, would face a predictable and severe adaptive problem – the kind of problem that selection would expectably and powerfully have addressed in the evolutionary past.

The most parsimonious explanation for the apparent absence of suicide among younger children, the severely cognitively impaired, and nonhuman animals, is that these populations lack the cognitive wherewithal to conceive and enact it.

{ Animal Sentience | PDF }

acrylic on canvas { Olivier Mosset, Untitled, 1970 }

This study documents that men and women experience and perform consumer shopping differently. […]

There is an abundant literature on sex differences in spatial abilities and object location that follow from the specific navigational strategies associated with hunting and gathering in the ancestral environment. In addition to sex differences in navigational strategies, the unique features of hunting and gathering may have influenced other aspects of foraging psychology that underlie sex differences in modern male and female shopping experiences and behaviors. […]

It is well accepted that humans do not simply develop new behaviors for every new situation we encounter but instead modify or extend existing behaviors to suit the new situation. Thus, the behaviors we exhibit in a modern and recently developed (i.e., with respect to an evolutionary timeframe) shopping mall, should be based on previously developed behaviors and skills. We believe, and study findings support this belief, that modern shopping behaviors are an adaptation of our species’ ancestral hunting and gathering skills. […]

For the most part, contemporary stereotypes of women in modern industrial countries perceive women as enjoying shopping more than men. Our research provides evidence that this popular stereotype exists because most shopping activities have a greater similarity to women’s traditional activities of foraging and gathering than they do to men’s traditional activity of hunting. The results of our study show that shopping has significantly more in common with gathering than it does with hunting.

{ Journal of Social, Evolutionary, and Cultural Psychology | Continue reading }

related { Hunter-gatherer lifestyle could help explain superior ability to ID smells }

In a mossy forest in the western Andes of Ecuador, a small, cocoa-brown bird with a red crown sings from a slim perch. […] Three rival birds call back in rapid response. […] They are singing with their wings, and their potential mates seem to find the sound very alluring. […]

This is an evolutionary innovation — a whole new way to sing. But the evolutionary mechanism behind this novelty is not adaptation by natural selection, in which only those who survive pass on their genes, allowing the species to become better adapted to its environment over time. Rather, it is sexual selection by mate choice, in which individuals pass on their genes only if they’re chosen as mates. From the peacock’s tail to the haunting melodies of the wood thrush, mate choice is responsible for much of the beauty in the natural world.

Most biologists believe that these mechanisms always work in concert — that sex appeal is the sign of an objectively better mate, one with better genes or in better condition. But the wing songs of the club-winged manakin provide new insights that contradict this conventional wisdom. Instead of ensuring that organisms are on an inexorable path to self-improvement, mate choice can drive a species into what I call maladaptive decadence — a decline in survival and fecundity of the entire species. It may even lead to extinction.

{ NYT | Continue reading }

art { Cy Twombly, Achilles Mourning the Death of Patroclus, 1962 }

Most people in industrialized societies grow up in core (parents only) families with few if any siblings. Based on an evolutionary perspective, it may be argued that this environment reflects a mismatch, in that the tribal setting offered a larger number of close affiliates. The present project examined whether this mismatch may have a negative impact on mental health. […]

The number of household members correlated with scores on good mental health at all ages tested (3, 5 and 8 years). […] Living with a single mother did not make any difference compared to two parents. Girls were slightly more responsive to the presence of siblings than boys. Household pets did not have any appreciable impact.

{ BMC Psychology | Continue reading }

The classic argument is that those of our ancestors who saw more accurately had a competitive advantage over those who saw less accurately and thus were more likely to pass on their genes that coded for those more accurate perceptions, so after thousands of generations we can be quite confident that we’re the offspring of those who saw accurately, and so we see accurately. That sounds very plausible. But I think it is utterly false. It misunderstands the fundamental fact about evolution, which is that it’s about fitness functions — mathematical functions that describe how well a given strategy achieves the goals of survival and reproduction. […]

Evolution has shaped us with perceptions that allow us to survive. But part of that involves hiding from us the stuff we don’t need to know. And that’s pretty much all of reality, whatever reality might be.

{ Quanta | Continue reading }

Venturing into novel terrain poses physical risks to a female and her offspring. Females have a greater tendency to avoid physical harm, while males tend to have larger range sizes and often outperform females in navigation-related tasks. Given this backdrop, we expected that females would explore a novel environment with more caution than males, and that more-cautious exploration would negatively affect navigation performance. […]

Findings support the idea that the fitness costs associated with long-distance travel may encourage females to take a more cautious approach to spatial exploration, and that this caution may partially explain the sex differences in navigation performance.

{ Human Nature | Continue reading }

In Women After All: Sex, Evolution, and the End of Male Supremacy, Melvin Konner argues that male domination is an anomaly of human history, not a natural state for the human species. Specifically, Konner suggests that male supremacy is largely an effect of an oppressive social arrangement, namely civilization, which began with the invention of agriculture when humans began to form permanent settlements. Permanent settlements enabled men to be able to accumulate resources and allowed population densities to increase mainly through higher birth rates. Higher population densities placed more intense pressure on the land’s resources. Therefore, it became necessary for men to form coalitions with neighbors to defend against intruders. Power became concentrated in the hands of a few men, leading to a stratified society where male supremacy and female subordination reigned and male violence and war intensified. Today, Konner argues that technology limits the need for the muscle and strength of men, and male domination has outlived its purpose and is maladaptive. Therefore, empowering women is the next step in human evolution. Through empowering women, equality between the sexes will be restored and man-made disasters, such as wars, sex scandals, and financial corruption, will significantly decrease or be eliminated since women (who Konner claims are less emotional than men) will be in positions of leadership and power.

{ Evolutionary Psychology | Continue reading }

We now have four good Darwinian reasons for individuals to be altruistic, generous or ‘moral’ towards each other. First, there is the special case of genetic kinship. Second, there is reciprocation: the repayment of favours given, and the giving of favours in ‘anticipation’ of payback. Following on from this there is, third, the Darwinian benefit of acquiring a reputation for generosity and kindness. And fourth, if Zahavi is right, there is the particular additional benefit of conspicuous generosity as a way of buying unfakeably authentic advertising.

{ Richard Dawkins | Continue reading }

photo { Todd Fisher }

A recent Norwegian study shows that men and women react differently to various types of infidelity. Whereas men are most jealous of sexual infidelity, so-called emotional infidelity is what makes women the most jealous. Evolutionary psychology may help explain why this may be. […]

Men and women over thousands of generations have had to adapt to different challenges that are related to reproduction. Infidelity is one such challenge. A man must decide whether he really is the father of his partner’s child, and if he should choose to invest all his protection and status resources on this child. Since the dawn of time men have grappled with paternity insecurity, since fertilization occurs inside a woman’s body.

According to the evolutionary psychology explanation, men’s jealousy is an emotional reaction to signs of sexual infidelity. The jealousy serves to reduce the chances that his partner is cheating, since he then monitors her more closely.

It’s a different story for the child’s mother. She knows for sure that she is the child’s mother, but she must ensure that the child’s father will provide their offspring with food and the security and social status it needs. The greatest threat for the woman is not that the man has sex with other women, but that he spends time and resources on women other than her.

{ Medical Xpress | Continue reading }

The ratio between the body circumference at the waist and the hips (or WHR) is a secondary sexual trait that is unique to humans and is well known to influence men’s mate preferences. Because a woman’s WHR also provides information about her age, health and fertility, men’s preference concerning this physical feature may possibly be a cognitive adaptation selected in the human lineage. […]

We analyzed the WHR of women considered as ideally beautiful who were depicted in western artworks from 500 BCE to the present. These vestiges of the past feminine ideal were then compared to more recent symbols of beauty: Playboy models and winners of several Miss pageants from 1920 to 2014. We found that the ideal WHR has changed over time in western societies: it was constant during almost a millennium in antiquity (from 500 BCE to 400 CE) and has decreased from the 15th century to the present. Then, based on Playboy models and Miss pageants winners, this decrease appears to slow down or even reverse during the second half of the 20th century.

The universality of an ideal WHR is thus challenged, and historical changes in western societies could have caused these variations in men’s preferences.

{ PLOS | Continue reading }

The “hygiene hypothesis” […] suggests that people in developed countries are growing up way too clean because of a variety of trends, including the use of hand sanitizers and detergents, and spending too little time around animals.

As a result, children don’t tend to be exposed to as many bacteria and other microorganisms, and maybe that deprives their immune system of the chance to be trained to recognize microbial friend from foe.

That may make the immune system more likely to misfire and overreact in a way that leads to allergies, eczema and asthma, Hesselmar says. […]

In their latest research, the researchers took a look at how people wash their dishes. […] In families who said they mostly wash dishes by hand, significantly fewer children had eczema, and somewhat fewer had either asthma or hay fever, compared to kids from families who let machines wash their dishes.

{ NPR | Continue reading }

photo { Daria Zhemkova photographed by Mario Kroes }